The present invention relates to an apparatus and method for simulating the in vivo mechanical environment to which living cells are subjected. More particularly, the present invention relates to a method and apparatus for imparting biaxial strain to living cells during their growth cycle.
Many living cells, such as those which form tissues including bone, ligament, tendon and muscle are subject to mechanical stress and deformation during the normal course of living. Such a dynamic environment is believed to be important to the growth and health of such cells. Similar mechanical forces which approximate those encountered in vivo are likewise believed to benefit cells grown in a tissue culture. These beneficial mechanical forces include biaxial compression and tension forces applied to the cells during their growth cycle.
The effect of such mechanical influences on cell growth and development is not yet well understood. Consequently, researchers are now investigating the effect of mechanical forces on cells by attempting to approximate, in vitro, the biaxial forces to which cells are subjected in vivo. Thus, in conducting this research it is useful to be able to generate uniform biaxial mechanical forces as well as biaxial forces which have various, predetermined ratios of non-uniformity.
Apparatuses which apply stretching forces to living cells are now known. Typically, these devices include a substrate, upon which cells may be mounted, which itself is adhered to an elastic membrane. When the membrane is stretched through the application of a tensioning force, some of the force is presumably transferred to the individual cells. In reality, however, the stretching forces often are not biaxially applied to the cells, and it is difficult to achieve forces which uniformly affect all of the cells of a given sample. In many cases the cells are subjected only to non-uniform strains. For research and other applications it is important that all cells in the culture experience the same strain.
One apparatus for applying mechanical forces to cells cultures utilizes the application of positive and negative pressure to a membrane upon which the cells are plated. It is generally believed that such pressure-induced deformation of a membrane will not apply a uniform strain to cells mounted upon the membrane at all levels of applied pressure. Moreover, the strain can be difficult to control as it is quite dependent on properties of the membrane. U.S. Pat. No. 4,851,354, however, does claim to achieve a substantially uniform application of biaxial strain to cells grown upon a membrane deformed by the application of pressure. But, Gilbert et al, 35th Annual Meeting, Orthopedic Research Society, p. 249 (Feb. 7, 1989) reports non-uniform strain with a similar pressure mechanism.
Accordingly, there is a need for an apparatus and method for applying to cultures of living cells biaxial forces which simulate an in vivo mechanical environment. It would also be useful to provide such an apparatus which could produce such forces uniformly throughout the cell culture, as well as forces which have selected, non-uniform strain profiles.
It is thus an object of the invention to provide an apparatus able to apply to living cells biaxial forces which approximate those encountered in vivo. It is also an object of the invention to provide such an apparatus which can impart to the cells uniform biaxial forces, as well as selectively non-uniform biaxial forces. A further object of the invention is to provide methods of utilizing such apparatuses to grow living cells in a mechanical environment which approximates that found in vivo. Other objects of the invention will be apparent to those skilled in the art upon review of this disclosure.